You can gain and lose 2-4 lbs easily just by being well-hydrated or dehydrated, or by being a little "sluggish" in the elimination department.

I often find I am down if I weigh myself on a Saturday morning but it's usually because I've had a few glasses of wine on Friday night. Even just 3 glasses can dehydrate me enough to lose 1-2 lbs.

Anyway, I agree with everyone else. Weight loss / change in diet and exercise - takes time. You gain muscle/weight, you lose fat/weight. Focus on how you feel and how you look. Use the scale for interest but try not to freak about it.